In general, a refrigerator includes: a main body that is divided into a freezing room and a cold-storage room; a door unit that rotationally opens and closes the front opening portions of the freezing room and the cold-storage room; and a refrigerating apparatus that cools the inside of the freezing room and the cold-storage room.
The refrigerating apparatus includes: a compressor that compresses a gas phase refrigerant into a high temperature and high pressure refrigerant; a condenser that condenses the gas phase refrigerant that has been compressed at the compressor into a liquid phase refrigerant; a capillary tube that changes the liquefied refrigerant into a low temperature and low pressure refrigerant; and an evaporator that vaporizes the refrigerant that has been liquefied into the low temperature and low pressure refrigerant at the capillary tube to thereby absorb evaporation latent heat and thus cool surrounding air. The refrigerating apparatus supplies the cooled air around the evaporation to the inside of the freezing room and the cold-storage room, using a blower, to thereby cool the inside of the freezing room and the cold-storage room.
Since a surface temperature of the evaporator that is provided in the refrigerating apparatus of this refrigerator is lower than the temperature in the refrigerator, water that exists in the internal air of the refrigerator is attached to the surface of the evaporator in the form of frost. Since the frost causes to decrease a heat exchange ability of the evaporator, a defrost heater is installed in order to remove frost that is attached to the evaporator.
Referring to FIGS. 1 and 2, a defrost heater that is installed in a refrigerator will be described as an example among various types of heaters.
As shown in FIG. 1, an evaporator 1 of a refrigerator is made of a tube 2 that is bent in a zigzag form and through which a refrigerant flows, and a number of fins 3 that enclose the tube 2 to perform a heat exchange function with respect to the tube 2. The number of the fins 3 are formed into a structure that a plurality of fins are formed by respective horizontal lines of the tube 2 or a structure that a plurality of vertical fins are formed into a single fin unit to enclose the whole horizontal lines. The tube 2 through which the refrigerant flows passes through the central portion of the number of the fins 3, to thereby improve a heat exchange performance.
Since frost is attached to the surface of the evaporator 1 of this refrigerator is covered with during performing a refrigerating cycle, a defrost heater that removes frost is provided.
A conventional defrost apparatus includes: first and second defrost heaters 4 and 5 that are bent in a zigzag form on the front and rear surfaces of the evaporator 1 and are mounted to be in a line contact with the fins 3; and a third defrost heater 6 that is mounted at the lower side of the evaporator 1. The conventional defrost apparatus executes a defrost cycle that removes frost formed on the surface of the evaporator 1 periodically.
In the case of the conventional defrost apparatus, the first and second defrost heaters 4 and 5 are installed to be in a line contact with the evaporator 1 and the third defrost heater 6 is installed at a distance from the evaporator 1 at the lower side of the evaporator 1.
In this case, the first to third defrost heaters 4, 5, and 6 can be formed of a sheath heater or glass heater, respectively. Heat that is produced in the sheath heater and glass heater melts frost that has been attached to the evaporator 1 in a radiation or convection method to thereby remove the frost.
In this way, since the first defrost heater 4 and the second defrost heater 5 are mounted on the front and rear surfaces of the evaporator 1 in the case of the conventional defrost apparatus, and the third defrost heater 6 is installed at the lower side of the evaporator 1, a heat emission temperature should be increased due to a temperature difference depending upon the positions, respectively.
However, since the first to third defrost heaters 4, 5, and 6 are in line contact with the evaporator 1 and installed at a distance from the evaporator 1 in the conventional technology, a problem of lowering a defrost efficiency has been caused. In addition, since the first to third defrost heaters 4, 5, and 6 respectively having a large heater capacity are required in order to improve a defrost performance, a problem of increasing electric power consumption has been caused.
In general, a sheath heater is fabricated by coiling a heat wire in a tube and charging high purity magnesium oxide whose heat insulation and heat conductivity are excellent in a high pressure state. Since the sheath heater is strong with respect to an external mechanical impact or shock, has a long life-time, and has no declination of an insulation capability even in the case of using it under the high temperature circumstances, it is known that the sheath heater is very safe electrically.
However, the sheath heater applied to a defrost heater restricts its heat emission area due to spatial restriction and has a high electric power (Watt) density in the heater. Accordingly, the sheath heater has a very high surface temperature characteristic but has a very low temperature response performance. As a result, there is a problem that the sheath heater is not converted into a refrigerating cycle quickly after completion of the defrost operation.
That is, since the defrost heater that uses a tubular type heater such as the sheath heater performs high temperature heat emission commonly, it may cause a problem in safety. In addition, since electric power of the defrost heater is turned off and a compressor is operated simultaneously when the defrost operation has been completed, the defrost heater has long cooling time that is taken to lower temperature of a refrigerant tube until a point in time when a refrigerating cycle of the refrigerating apparatus is reactivated, that is, down to 0 (that is, a heater temperature response performance is slow), there is a problem that the whole defrost cycle is prolonged. That is, if the defrost cycle is prolonged, it cannot be converted from the defrost cycle into the refrigerating cycle after completion of defrost. Accordingly, there is a problem that a freezing performance falls.
In addition, since a conventional tube shaped defrost heater is thick, it is limited to install and use the defrost heater in various defrost apparatuses. Further, there has been a problem that an assembly performance and a productivity fall.
Meanwhile, in order to improve the problems of the defrost heater that uses the sheath heater, the Korean Patent No. 584274 has proposed a defrost apparatus including: an evaporator having a fin-tube; and a defrost heater unit having first and second defrost heaters that have an insulation film and a heater wire that is coated on the insulation film, and whose surface is formed of a corrugated surface, to thus be attached on the front and rear surfaces of the evaporator, and to thereby remove a layer of frost produced on the surface of the evaporator, in which the defrost heaters are depressed and fixed by the corrugated surface of the defrost heaters between both side surfaces of the evaporator and an inner fixed portion of the cold-storage room facing the evaporator.
In the case of the defrost heater, the heater wire of a zigzag form is coated by the insulation film that has an unevenness corrugated surface so that the tube is applied in the structure of the evaporator arranged at the outside of the fins, and the defrost heater is mounted in a tube bracket and a tube that are vertically installed on both sides of the defrost heater, using an adhesive.
However, since the tube bracket has a structure of the whole evaporator with a trapezoidal structure so that a number of tubes that are vertically and horizontally arranged at crossing points of straight lines and curved lines are piercingly inserted at the left/right sides of an “S” shape of the tubes, both side ends of the defrost heater of the corrugated surface shape preferentially contact the tube brackets of both sides of the defrost heater. Accordingly, the defrost heater has a structure that is difficult to be in substantially direct contact with the tubes.
In addition, the heater wire of the defrost heater is made of a wire having a high thermal density and expensive nichrom. Accordingly, the outer circumference of the wire should be primarily insulated and coated to thereby cause a low heat transfer efficiency. In addition, a thick insulation film should be used to thereby also cause a low heat transfer efficiency.
Meanwhile, the Korean Utility-model Publication No. 1998-10548 discloses a defrost apparatus in which a carbon paste is formed in a plate shaped member in a pattern form of a parallel connection structure as a heat emission element, and a linear electric conductor is connected between both ends of the defrost apparatus.
However, the defrost apparatus that uses a carbon heater as the heat emission element, has the difficulty in realizing a heater of high capacity of 200 W, and performs heat emission of 40 or so generally. As a result, if the carbon heater is used for the defrost apparatus, there is a problem that a low temperature response performance is slow similarly to that of the sheath heater.
In addition, when the carbon heater is coated by a plastic film for insulation, there is a problem that the carbon heater becomes weak for thermal shock. Further, the carbon that acts as a heat emission element has a shortcoming that physical properties are changed in use long hours.
Meanwhile, when the sheath heater is used as the defrost heater, heat emission is attained up to about 600° C. In this connection, since R11 or R22 that is a current non-environment-friendly refrigerant has a high ignition point, the sheath heater can be used without causing a big problem. However, the non-environment-friendly refrigerant cannot be adopted for products that are manufactured from Jan. 1, 2010. Further, even in the case of the existing products that employ the non-environment-friendly refrigerant, use of R22 is prohibited according to the Uruguay Round agreement from 2020 onward, and only environment-friendly refrigerants such as R600a (isobutane: CH(CH3)3); and Refrigerant boiling point: 460° C.) will be allowed for use by SA53 that is defrost heater requirements of the Chapter 5 of the UL (Underwriters Laboratories Inc) 250.
According to the UL 250 standards, when a refrigerant has been leaked, the surface temperature of a defrost heater is restricted to be lower by 100 than an ignition point of the refrigerant, in order to prevent firing of the refrigerant. Therefore, when using new refrigerants such as R600a, R600 (n-butane: CH3CH2CH2CH3: Refrigerant boiling point: 365° C.) and R290 (propane; CH3CH2CH3; Refrigerant boiling point: 470° C.) unlike the existing refrigerants, it is required that the surface temperature of the heater should be controlled not more than almost 270° C. because of the ignition point of the refrigerant.
However, when the existing sheath heater or glass heater having the high power density is used as the heater, it is difficult to satisfy the surface temperature of the heater as a limited temperature that is newly specified by the UL 250 standards for the ignition point of the refrigerant, that is, a condition that is lower by 100 than the ignition point of the refrigerant. In this case, if temperature is risen, fire may occur by the leaked refrigerant.